DESCRIPTION: (Applicant's Abstract) Sedative/anxiolytic misuse and abuse are serious problems in our society. The most common of these drugs, benzodiazepine and barbiturates, are positive allosteric modulators of GABA-A receptor function. GABA-A receptors are heteropentameric assemblies from at least five subunit families (alpha 1-6, beta 1-4, gamma 1-3, delta and epsilon). In vitro studies have shown that GABA-A receptor subunit composition is critical to the actions of GABA ligands. The presence of a delta subunit in recombinant GABA-A receptors confers increased sensitivity to GABA and insensitivity to benzodiazepines and neurosteroids. Recently, mice lacking a functional GABA-A delta subunit have been created. Neurosteroid-induced sleep time is decreased in these animals, in direct contrast to predictions based on recombinant receptors. This suggests that multiple compensatory changes in subunit composition may occur as a result of delta subunit deletion. This application will use the drug discrimination paradigm to examine the receptor-mediated subjective discriminative stimulus effects of diazepam in delta subunit knockout mice. The discriminative stimulus effects of a drug are a function of specific receptor interactions and are believed to be related to abuse liability. The first specific aim of this proposal is to establish a diazepam discrimination in delta knockout mice and wild-type controls. It is hypothesized that both strains of mice will successfully acquire the discrimination but will differ in the time required to reach criteria performance. The second major aim is to determine if the delta subunit plays a role in the discriminative stimulus effects of diazepam and other GABA-A modulators. Based on data showing altered neurosteroid effects in delta knockout mice, we believe that each strain will exhibit a unique substitution profile of GABA-A modulators for diazepam. These data will provide an important characterization of the discriminative stimulus effects of diazepam in delta subunit knockouts and would be the first study of the discriminative stimulus effects of a drug in any knockout mouse. Additionally, the results from this study may help to elucidate how changes in specific subunit alterations of the GABA receptor translate into changes in the behavioral effects of sedative/anxiolytic drugs.